A violation of the uncertainty principle implies a violation of the second law of thermodynamics

Uncertainty relations state that there exist certain incompatible measurements, to which the outcomes cannot be simultaneously predicted. While the exact incompatibility of quantum measurements dictated by such uncertainty relations can be inferred from the mathematical formalism of quantum theory, the question remains whether there is any more fundamental reason for the uncertainty relations to have this exact form. What, if any, would be the operational consequences if we were able to go beyond any of these uncertainty relations? We give a strong argument that justifies uncertainty relations in quantum theory by showing that violating them implies that it is also possible to violate the second law of thermodynamics. More precisely, we show that violating the uncertainty relations in quantum mechanics leads to a thermodynamic cycle with positive net work gain, which is very unlikely to exist in nature.Comment: 8 pages, revte

Bacteriology in Veterinary Practice

In the past undergraduates in veterinary medicine were not able to envisage any practical use for their laboratory training in bacteriology. When a practitioner required a cultural examination it was necessary to submit the specimen to an established laboratory and three or more days would elapse before a reply was received. There has been a marked change in this approach to bacteriology within the last few years and it is the purpose of this presentatioll to explain how bacteriological methods can be used in a clinical practice

Generalization of entanglement to convex operational theories: Entanglement relative to a subspace of observables

We define what it means for a state in a convex cone of states on a space of observables to be generalized-entangled relative to a subspace of the observables, in a general ordered linear spaces framework for operational theories. This extends the notion of ordinary entanglement in quantum information theory to a much more general framework. Some important special cases are described, in which the distinguished observables are subspaces of the observables of a quantum system, leading to results like the identification of generalized unentangled states with Lie-group-theoretic coherent states when the special observables form an irreducibly represented Lie algebra. Some open problems, including that of generalizing the semigroup of local operations with classical communication to the convex cones setting, are discussed.Comment: 19 pages, to appear in proceedings of Quantum Structures VII, Int. J. Theor. Phy

Largest separable balls around the maximally mixed bipartite quantum state

For finite-dimensional bipartite quantum systems, we find the exact size of the largest balls, in spectral $l_p$ norms for $1 \le p \le \infty$, of separable (unentangled) matrices around the identity matrix. This implies a simple and intutively meaningful geometrical sufficient condition for separability of bipartite density matrices: that their purity \tr \rho^2 not be too large. Theoretical and experimental applications of these results include algorithmic problems such as computing whether or not a state is entangled, and practical ones such as obtaining information about the existence or nature of entanglement in states reached by NMR quantum computation implementations or other experimental situations.Comment: 7 pages, LaTeX. Motivation and verbal description of results and their implications expanded and improved; one more proof included. This version differs from the PRA version by the omission of some erroneous sentences outside the theorems and proofs, which will be noted in an erratum notice in PRA (and by minor notational differences

Compressibility of Mixed-State Signals

We present a formula that determines the optimal number of qubits per message that allows asymptotically faithful compression of the quantum information carried by an ensemble of mixed states. The set of mixed states determines a decomposition of the Hilbert space into the redundant part and the irreducible part. After removing the redundancy, the optimal compression rate is shown to be given by the von Neumann entropy of the reduced ensemble.Comment: 7 pages, no figur

Risks of Sharing Cyber Incident Information

Incident information sharing is being encouraged and mandated as a way of improving overall cyber intelligence and defense, but its take up is slow. Organisations may well be justified in perceiving risks in sharing and disclosing cyber incident information, but they tend to express such worries in broad and vague terms. This paper presents a specific and granular analysis of the risks in cyber incident information sharing, looking in detail at what information may be contained in incident reports and which specific risks are associated with its disclosure. We use the STIX incident model as indicative of the types of information that might be reported. For each data field included, we identify and evaluate the threats associated with its disclosure, including the extent to which it identifies organisations and individuals. The main outcome of this analysis is a detailed understanding of which information in cyber incident reports requires protection, against specific threats with assessed severity. A secondary outcome of the analysis is a set of guidelines for disciplined use of the STIX incident model in order to reduce information security risk

Physical implementation of entangling quantum measurements

We clarify the microscopic structure of the entangling quantum measurement superoperators and examine their possible physical realization in a simple three-qubit model, which implements the entangling quantum measurement with an arbitrary degree of entanglement.Comment: 6 pages, 2 fihure

Optimal Quantum Cloning Machines

We present Quantum Cloning Machines (QCM) that transform N identical qubits into $M>N$ identical copies and we prove that the fidelity (quality) of these copies is optimal. The connection between cloning and measurement is discussed in detail. When the number of clones M tends towards infinity, the fidelity of each clone tends towards the optimal fidelity that can be obtained by a measurement on the input qubits. More generally, the QCM are universal devices to translate quantum information into classical information.Comment: 4 pages, Latex, 1 postscript figure, (very) minor modification

Improved quantum algorithms for the ordered search problem via semidefinite programming

One of the most basic computational problems is the task of finding a desired item in an ordered list of N items. While the best classical algorithm for this problem uses log_2 N queries to the list, a quantum computer can solve the problem using a constant factor fewer queries. However, the precise value of this constant is unknown. By characterizing a class of quantum query algorithms for ordered search in terms of a semidefinite program, we find new quantum algorithms for small instances of the ordered search problem. Extending these algorithms to arbitrarily large instances using recursion, we show that there is an exact quantum ordered search algorithm using 4 log_{605} N \approx 0.433 log_2 N queries, which improves upon the previously best known exact algorithm.Comment: 8 pages, 4 figure

Improving Detectors Using Entangling Quantum Copiers

We present a detection scheme which using imperfect detectors, and imperfect quantum copying machines (which entangle the copies), allows one to extract more information from an incoming signal, than with the imperfect detectors alone.Comment: 4 pages, 2 figures, REVTeX, to be published in Phys. Rev.